1. Field of the Invention
The present invention relates to an ink-jet recording device, a driving circuit for an ink-jet printing head and a method for driving the ink-jet printing head. More particularly, the present invention relates to a serial type ink-jet recording device, a driving circuit for a color ink-jet printing head and a method for driving the color ink-jet printing head.
2. Description of the Related Art
Ink jet printing has attracted special attention since it is capable of printing an image on plain paper without contact of the printing head with the paper. Generally, an ink jet printer system uses a simple printing process and makes almost no vibration and noise during an operation. Also, the ink jet printer system can be suitably applied to color image printing. Thus, the ink jet printer system is considered as being advantageous over other existing printing systems.
These days, an ink jet printer system using ink-jet printing heads is widely used as, for instance, a printer for a computer, facsimile, a word processor, and scientific instruments. In piezoelectric type ink jet printing heads, a piezoelectric actuator is used to force out ink drops from nozzles in accordance with print signals by applying a force to ink within ink chambers through actuation of an actuator. In this manner, dots of ink drops are formed and an image may be recorded on a recording medium with a high speed, high resolution and high quality.
Some ink-jet printing device using a piezoelectric actuator have a structure in which piezoelectric elements are actuated by selecting an appropriate pulse from a pulse group comprising a plurality of voltage pulses as disclosed in Japanese Laid-Open Patent Application No.57-160654. Ink drops forced out from respective nozzles by the movement of the thus actuated piezoelectric actuator are combined together in the air to form one ink drop of various colors and is applied to a recording medium to make a dot of the color on the recording medium.
Also, as disclosed in Japanese Laid-Open Patent Application No.62-267150, some ink-jet printing device have a structure in which the volume of an ink drop is controlled so that a color tone of a pixel is distinctively increased in accordance with an increment of input signals of optical density for each of the ink-jet printing heads having nozzles of different sizes, and one pixel is filled with one or more ink drops ejected from the nozzles of different size.
Moreover, Japanese Laid-Open Patent Application No.63-251241 discloses an ink-jet printing device having a signal changing unit which changes a falling-time constant of a driving pulse, which is used for returning an ink chamber to an initial state, in accordance with a voltage value so that the return of a meniscus of the nozzle proceeds at a proper speed without exceeding a predetermined distance after a discharging process of ink drops from nozzles of the ink chamber, which is carried out by rapidly decreasing the volume of the ink chamber (or rapidly increasing the pressure of the ink chamber).
Further, Japanese Laid-Open Patent Application No.59-42965 discloses an ink-jet printer, in which ink drops are discharged by pressurizing ink contained in an ink chamber by applying a pulse voltage to piezoelectric elements, having an adjusting means which is capable of adjusting at least one of a pulse rising-time and time of the pulse.
However, as for the above-mentioned ink-jet printing device in which the piezoelectric elements are actuated by selecting an appropriate pulse from a pulse group, the number of electric circuits of a driving circuit are necessary for selecting the appropriate pulse, which correspond to each of the piezoelectric elements, is increased when the number of nozzles used for an ink-jet printing head is increased. Thus, high-integration of an ink-jet printing head may become difficult to achieve. Also, the size of the entire driving circuit becomes large and the number of leads used for connecting each circuit is accordingly increased. This may lead to an increase of the manufacturing cost of the ink-jet printing device.
Moreover, according to the above-mentioned ink-jet printing device disclosed in Japanese Laid-Open Patent Application No.62-267150, since a pixel is filled by continuously ejecting ink drops using a certain number of pulse groups, the response frequency of the ink ejection is necessarily multiplied by the spatial frequency of a pixel formed on a recording medium, and hence an extremely high response frequency is required.
As for the ink-jet printing device disclosed in Japanese Laid-Open Patent Application No.63-251241, since the falling-time constant is not significantly changed when a pulse voltage is large, the return of a meniscus does not exceed a predetermined distance if a volume of discharged ink is increased. However, if the pulse voltage is raised, the volume of discharged ink is increased due to the increase of energy to the piezoelectric elements regardless of the falling-time constant and unnecessary satellite ink drops are generated. Thus, the recording position of an ink drop on a recording medium is different when the pulse voltage is raised or increased, and hence a positioning accuracy of a dot and image quality produced is deteriorated.
With regard to the ink-jet printer disclosed in Japanese Laid-Open Patent Application No.59-42965, the pulse voltage may be optimized by adjusting the rising-time or the duration of the pulse voltage. However, when it is necessary to change the pulse voltage in order to change a dot size or to control the dot size by changing a volume of discharged ink according to a type of recording medium or ink used, it is not possible to stably discharge the ink by adjusting the rising-time or the duration of the pulse.